Environment of Early life on Earth 2 – eLIFE2

During the course of project ANR-Blan-eLIFE that ended November 2009, we have obtained, among others, two results of great significance for our understanding of the interplay between biological processes and the evolution of the primitive atmosphere and oceans prior to the Great Oxidation Event at about 2.4 Ga. First, the discovery of a new type of microbial sulfur processor thriving on mass-independently fractionated elemental sulfur (MIF-S) derived from the photolysis of volcanic sulfur compounds in the Early Archean atmosphere (Philippot et al., 2007, Science) and second, the identification for the first time of noble gas signatures dating back to the Early Archean (Pujol, in review, Nature), therefore bearing important information on the state of the ancient atmosphere and on mantle-crust-atmosphere interactions in the Hadean and Archean. These results were obtained on pristine drill core samples (Pilbara Drilling Project) from one locality, the 3.5 Ga old chert-barite deposit of the Dresser Formation, Western Australia. Similar studies in rocks of different ages and origin would provide great potential for elucidating further the nature and evolution of the primitive atmosphere and its interplay with microbial life and emerging continental surfaces. This is the objective of the present project eLIFE2.
We have obtained another drill core (Barbeton Barite Drilling Project, BBDP) from the 3.2 Ga chert-barite unit of the Mapepe Formation, Barberton Greenstone Belt, South Africa, and identified three paleosols from the Fortescue Group, Western Australia; the reference Mt Roe Basalt (RYE et al., 1995) at 2.78 Ga and two newly discovered paleosols from the 2.74 Ga Kylena and the 2.68 Ga Jeerinah Formation. Preliminary investigations revealed that BBDP drill core contains abundant barite and two spherule layers (S1, S2) attributed as fallout signature of large interterrestrial impacts (LOWE et al., 2003) and that one paleosol contains local layers of carbonaceous material and CH4-bearing inclusion fluids. If confirmed, the later would be in line with models advocating for a peak of production of atmospheric methane during the Late Archean.
During previous eLIFE project, we have used, adapted and developed several state-of-the-art techniques and analytical protocols, which now allow analysing minute amounts of inclusion fluids (noble gas) and organo-(bio)mineral compounds (multiple S- and N- isotopes) preserved in rocks samples. In addition, specific protocol adapted to combined high spatial resolution analysis (Raman spectroscopy, SEM-FIB-TEM, (nano)SIMS, synchrotron-based techniques) have been tested and optimized. New from the eLIFE project, however, is the collaboration with a team from IPG-Paris (F. Fluteau and G. Lehir) specialized in numerical simulations of paleoclimate changes and geochemical modelling of environmental changes affecting the atmosphere-hydrosphere system.
The rationale of eLIFE2 is to constrain the parameters that are of relevance on the composition and evolution of the Earth’s hydrosphere and atmosphere during the Archean eon using climate and geochemical numerical inversion of (bio)geochemical observables extracted from the rock record by three teams from eLIFE that have already work together in in a fruitful and very productive way. These are the Noble Gas Geochemistry team of CRPG-Nancy (B. Marty, M. Pujol), the lab of Geochemistry of Stable Isotopes of IPG-Paris (M. Ader and P. Cartigny), and the lab of Modern and Primitive Geobiosphere of IPG-Paris (M. Gérard and P. Philippot).